l. Field of the Invention
The present invention relates generally to an integrally sintered ceramic complex and a method of manufacturing the same, which ceramic complex is suitable for use as a substrate of a surface acoustic wave device.
2. Description of the Prior Art
In general, a surface acoustic wave device is used as a filter device or delay line and the distance between input and output transducers thereof is selected in accordance with a desired delay time.
An ordinary surface acoustic wave divice is formed in such a manner that input and output transducers consisting of, for example, a pair of interdigital electrodes are mounted on the major surface of a piezoelectric substrate, which is made of ceramic and serving as a surface acoustic wave propagation medium, with a predetermined distance therebetween.
With such a prior art surface acoustic wave device, a surface acoustic wave generated at the input transducer arrives at the output transducer through the propagation medium and then is derived as an output signal from the latter. In this case, however, a part of the surface acoustic wave propagates beyond the output transducer to the end of the propagation medium, is then reflected thereon, returned to the output transducer and then derived as an output signal therefrom. Therefore, the frequency characteristics of the surface acoustic wave device is affected by the reflected acoustic wave or undesired acoustic wave to have a curve with ripples in its pass band. Therefore, in practice it is necessary to reduce or attenuate the undesired acoustic wave components as much as possible.
As a method to reduce the undesired wave components there has been proposed such a treatment that, on the both end portions of a surface acoustic ultrasonic wave propagation medium such as a piezoelectric substrate in its surface acoustic (ultrasonic) wave propagation direction, there are provided ultrasonic wave absorbing members made of such as polyurethane.
As another method of reducing the undesired reflected wave components, there has been also proposed to roughen both the end portions of the piezoelectric substrate, or to cut both the ends of the piezoelectric substrate obliquely with respect to the surface acoustic wave propagation direction so as to prevent the reflected wave on the both ends from being propagated reciprocally.
However, with any of the prior art methods it is rather complicated to work the piezoelectric substrate for reducing the undesired wave components, and also when some of the methods are combined so as to greatly reduce the undesired wave component, it becomes much complicated to manufacture such a piezoelectric substrate.